This invention relates to water-based emulsions of organopolysiloxane resins which are useful in coating applications where aqueous emulsions are preferable over traditional organic solvent based systems. The present invention provides both water-based silicone emulsions as well as methods for producing such compositions.
Silicone resins are often selected for applications requiring premium properties. These organopolysiloxane resins are known to offer outstanding endurance to environmental conditions such as weathering and extreme heat and cold. Silicone resins have found utility in a variety of applications such as pressure sensitive adhesives and release coatings. Furthermore, they have been found to be particularly useful in the paint industry which is continually seeking coating formulations which offer premium properties. Silicone resins solutions have previously been used in the paint coatings industry as vehicles and binders which are a necessary part of quality paint formulations.
Heretofore silicone resins were ordinarily supplied to formulators in solutions, that is to say, the resin consisted of so many parts by weight of silicone solids in some organic solvent such as xylene or toluene. However, recently the use of such organic solvents has been discouraged due to escalating costs for organic materials and increased concern for environmental considerations. Organic solvent based silicone resins often required the use of costly and cumbersome pollution abatement procedures and equipment. Thus there has been a trend in recent years for silicone resin systems which are water-based and therefore not dependent upon organic solvents.
However, such silicone resins which have been found to have particular utility in the art of paints and other coatings have often been immiscible or otherwise incompatible with aqueous coating systems. The present invention provides for the first time silicone resins which can be readily dispersed into water-based emulsion compositions thereby providing the beneficial properties of silicone resins without the cumbersome necessity of unduly large amounts of organic solvents.
As noted above, silicone resins are intended as high performance coating vehicles which can be used in high temperature-resistant coatings and will generally outperform conventional organic resins in similar applications. Those skilled in the art will recognize that there are a number of silicone resins which can be utilized in coating applications. Those silicone resins provided in U.S. Pat. Nos. 4,028,339 and 4,056,492 (both issued to Merrill) are examples of resins which can be made part of the water-based emulsion compositions of the present invention. Both of these patents are hereby incorporated by reference.
Previously known silicone resin emulsions have been successfully utilized in coating glass fabric, however, such compositions require the use of nonionic emulsifiers such as alkylphenoxy polyethoxyethanol. In such a system there is generally required approximately one part emulsifier for each nine parts of resin solids. When this type of emulsion technology is attempted in conjunction with the resin coating formulations discussed herein, as required by paint formulators, residual emulsifier is entrained in the coating and has a significant deleterious effect on such coatings at elevated temperatures.
The present invention, on the other hand, utilizes an emulsion system based upon a combination of anionic emulsifiers and certain methylcellulose ether compositions. The total emulsifier requirement for the emulsions of the present invention is generally in the range of approximately 0.5 to 2 percent based upon the weight of the silicone resin solids as compared to approximately 11% in the aforementioned emulsions. Furthermore, the reduction in organic emulsifier still enables the silicone resin film to function satisfactorily as a coating. Additionally, it seems that the use of methylcellulose agents enables the water-based compositions to coat out more uniformly as compared to the above-described emulsions utilizing nonionic emulsifiers.
It is therefore a primary object of the present invention to provide water-based emulsions of organopolysiloxane resins which are useful in coating formulations.
It is another object to provide an emulsifier system comprising a combination of anionic and methyl cellulose ether emulsifiers which are effective for dispersing silicone resins in a water-based coating system.
It is another object to provide a process for producing water-based silicone resin emulsions.
These and other objects will become apparent to those skilled in the art upon consideration of the accompanying description and claims.